SECRETORY PHOSPHOLIPASE-A(2) IS NOT REQUIRED FOR ARACHIDONIC-ACID LIBERATION DURING PLATELET ACTIVATION

The subcellular localization of secretory phospholipase A2 (sPLA2) and cytosolic phospholipase A2 (cPLA2) in resting and activated platelets , and their involvement in arachidonic acid liberation during platelet activation, were studied. The amounts of sPLA2 and cPLA2 recovered we re not modified during platelet activation. sPLA2 was mainly associate d with the organelles of resting platelets (71 % of total activity) an d was released into the extracellular medium during cell activation (6 0% of total activity), whereas the majority of cPLA2 was localized in the cytosol of resting and activated platelets. The secretion of sPLA2 correlated with the release of ATP. sPLA2-depleted platelets aggregat ed as much as control platelets and produced similar amounts of thromb oxane B2 upon thrombin activation. These results indicate that sPLA2 i s not involved in the liberation of arachidonic acid during platelet a ctivation.